I/R injury may develop in conditions in which the
blood and oxygen supply to a tissue is transiently disrupted and then restored. Hepatic I/R injury is a potentially fatal complication of liver surgery (including liver transplantation). Substances that improve hypoxia tolerance selleck chemicals llc may also protect against I/R injury. CBs induce hypomotility and hypothermia, both of which result in reduced oxygen demand. The metabolic effects of CBs that promote energy storage and reduce energy expenditure (discussed previously) may also reduce oxygen demand. There is evidence that endocannabinoids acting via CB2 protect against hepatic I/R injury.99, 100 In mice, segmental ischemia followed by reperfusion (but not ischemia alone) markedly increased the hepatic levels of AEA and 2-AG, which correlated with the severity of tissue damage.99
I/R-induced tissue damage, including neutrophil infiltration and lipid peroxidation, was attenuated by pretreatment with JWH-133 in wild-type mice but not in CB2−/− mice, in which the damage was more severe than that in wild-type littermates.99 Another potent and selective CB2 agonist, HU-308, caused similar effects and also attenuated I/R-induced hepatocyte apoptosis and mitigated the tumor necrosis factor-α–induced expression of cell adhesion molecules (intercellular cell adhesion molecule 1 and vascular cell adhesion molecule 1) in hepatic sinusoidal endothelial cells.100 Thus, CB2 agonists may afford protection at multiple levels against I/R injury; this highlights their therapeutic find more potential. PD98059 CB1 receptor blockade also protects the liver from I/R injury and superimposed endotoxaemia.101 In one study, rats subjected to lipopolysaccharide plus
I/R had an immediate increase in CB1 expression in perisinusoidal hepatocytes. Rimonabant treatment reduced both tissue necrosis and serum alanine aminotransferase levels in the late phase of reperfusion and attenuated the oxidative injury.101 Further studies with peripherally restricted CB1 receptor antagonists could reinforce the therapeutic potential of this approach. Hepatic encephalopathy is a neuropsychiatric syndrome that may accompany acute liver failure. The underlying mechanisms are not completely understood, although there is evidence for the pathogenic role of ammonia, alterations in various central neurotransmitter systems, and altered cerebrovascular function. Mice with thioacetamide-induced fulminant liver failure have elevated brain 2-AG levels. The treatment of such mice with 2-AG or the CB2 agonist HU-308 improved the neurological score and cognitive function, and these effects were blocked by a CB2 antagonist. The beneficial effects of CB2 agonists could be mimicked by treatment with the CB1 antagonist rimonabant.